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Sunday 19 June 2016

Disk Brake

UA-29869588-1

Disk Brake

Introduction

The meaning of a break means interrupt (continuity, sequence, or course). In Automobile we use the term break as the interruption of speed. In a little over a hundred years since the automobile took hold of people's imagination, technologies designed to make them accelerate faster and reach higher speeds have evolved with a fury the likes of which we can only see in the aeronautics industry. Still, despite chargers, turbochargers, twin turbochargers or NOX, there are limits which cannot be surpassed by a land based vehicle in terms of speed, be it because of technological limitations or the laws of physics. 

Not the same can be said about the rather unseen part of the automotive evolution: brakes. The only limitations imposed to them are in connection with the human body's ability to withstand rapid decelerations. Otherwise, it would be a lot easier stopping a car than making it go insanely fast. 

Whether they come in the form of drum brakes, as was the case in the dawn of the automobile, or as discs, the brakes have been the horsepower's companion throughout the decades, each pulling the evolution of the car in different directions. 

Types of Brake

There are several types of brakes, but our goal here is not to present their features. We will only take you through a slow, slow journey to the beginning of the braking systems. As for who came up with the idea of a braking system, no individual person can be credited for it. As the saying goes, what goes up must come down, or to paraphrase it, what goes fast, must stop. It was only obvious that whoever made a moving object, devised a stopping system as well. So it's rather a matter of who brought what to the idea, than who actually invented it. 
·         Wooden Block

The early braking systems to be used in vehicles with steel rimmed wheels consisted of nothing more than a block of wood and a lever system. When he wanted to stop, the driver had to pull the lever located next to him and make the wooden block bear against the wheel. 

The method proved effective in both horse drawn or steam powered vehicles. It started becoming obsolete towards the end of the 1890s, when the Michelin brothers began replacing steel rimmed wheels with the rubber tire. The wood block method, needless to say, was useless in conjunction with rubber. 
·         Slowly Grinding to a Halt


The drum based braking system can be considered the forefather of the modern day break. A forefather who is still alive, as drum brakes are still in use today. 

The man largely credited with the development of the modern day drum brake is French manufacturer Louis Renault, in 1902. Still, crude concepts of the drum existed before that. Wilhelm Maybach had used a similar, yet simpler design a year earlier. Even prior to that, in 1899, Gottlieb Daimler came up with the idea to wrap a cable around a drum and anchor it to the vehicles chassis. The forward motion of the car tightened the cable, making it easier for the driver to pull the lever and get the wood block to do its work. What Daimler came up with is called servo assistance and is still in use today, with the required enhancements, obviously. 

These types of braking systems were all external, a feature which soon turned into a problem. Dust, heat and even water rendered them less effective. It was time for the internal expanding shoe brake. By placing the shoes inside the drum brake, dust and water were kept out, allowing the braking process to remain effective


·         Hydraulic Power

The end of the mechanically-activated brakes came in 1918, when Malcolm Loughead, one of the founders of what later was to become Lockheed Aircraft Corporation, came up with the idea. Loughead put together a four-wheel hydraulic-brake system for cars. This system used fluids to transfer the force on the pressed pedal to the pistons and then to the brake shoes. 

The four-wheel hydraulic system was first used on the 1918 Duesenberg and quickly caught on, mostly thanks to the fact that it made braking much easier than in a mechanical system. By late 1920s, this system was fitted on most high-priced vehicles and soon after it expanded to most of the automotive world. 

·         The Disc
As the vehicles spilled out the assembly plants, they started becoming both faster and heavier. Hydraulic drum based brakes were effective, but they had a tendency to ineffectively distribute heat. This feature made room for the creation of the disc braking system


Even if it came to be, basically, at around the same time with the drum brake system, the disc had to go a long way before getting a place in the spotlight. First patented in 1902 by William Lanchester, the disc became popular in the 1950s. 

Using the disc brake in conjunction with Loughead hydraulics, Chrysler became the first manufacturer to implement the system on its vehicles (Imperial). In Europe, the system was adopted by Jaguar (C-Type) and Citroen (DS).

Still, the system was dropped for a few years in the US, as it still required some significant effort from the driver to operate it. It was only in 1964 when it made its final comeback, featured on the Studebacker Avanti. This time it succeeded. 

The difference was made by the development of the power braking system. By assisting the movement of the piston in the master cylinder, the driver no longer had to apply as much pressure to get the car to stop effectively. 
·         ABS (Anti blockier system),  

The evolution of the brakes themselves has since slowed down. Additional systems though took off. ABS (Anti blockier system), electronic brake-force distribution (EBD), brake assist and many other systems have come to help braking become as effective and as safe as it can be. Still, the foundations first set in the early 1900s remain the basis for modern day brakes.

Disk Brake
A disc brake is a type of brake that uses calipers to squeeze pairs of pads against a disc in order to create friction that retards the rotation of a shaft, such as a vehicle axle, either to reduce its rotational speed or to hold it stationary. The energy of motion is converted into waste heat which must be dispersed. Hydraulic disc brakes are the most commonly used form of brake for motor vehicles but the principles of a disc brake are applicable to almost any rotating shaft.
Compared to drum brakes, disc brakes offer better stopping performance because the disc is more readily cooled. As a consequence discs are less prone to the brake fade caused when brake components overheat. Disc brakes also recover more quickly from immersion (wet brakes are less effective than dry ones).
Most drum brake designs have at least one leading shoe, which gives a servo-effect. By contrast, a disc brake has no self-servo effect and its braking force is always proportional to the pressure placed on the brake pad by the braking system via any brake servo, braking pedal, or lever. This tends to give the driver better "feel" and helps to avoid impending lockup. Drums are also prone to "bell mouthing" and trap worn lining material within the assembly, both causes of various braking problems.
The brake disc (or rotor in American English) is usually made of cast iron, but may in some cases be made of composites such as reinforced carbon–carbon or ceramic matrix composites. This is connected to the wheel and/or the axle. To retard the wheel, friction material in the form of brake pads, mounted on the brake caliper, is forced mechanically, hydraulically, pneumatically, or electromagnetically against both sides of the disc. Friction causes the disc and attached wheel to slow or stop.
The development of disc-type brakes began in England in the 1890s, but they were not practical or widely available for another 60 years. Successful application required technological progress, which began to arrive in the 1950s, leading to a critical demonstration of superiority at the Le Mans auto race in 1953. The Jaguar racing team won, using disc brake equipped cars, with much of the credit being given to the brakes' superior performance over rivals from firms like Ferrari, equipped with drum brakes. Mass production quickly followed with the 1955 Citroën DS.

History of Disk Brake
Development of disc brakes began in England in the 1890s. The first caliper-type automobile disc brake was patented by Frederick William Lanchester in his Birmingham factory in 1902 and used successfully on Lanchester cars. However, the limited choice of metals in this period meant that he had to use copper as the braking medium acting on the disc. The poor state of the roads at this time, no more than dusty, rough tracks, meant the copper wore quickly making the system impractical.
The American Crosley Hot Shot is often given credit for the first production disc brakes. For six months in 1950, Crosley built a car with these brakes, and then returned to drum brakes. Lack of sufficient research caused reliability problems, such as sticking and corrosion, especially in regions using salt on winter roads.  Drum brake conversions for Hot Shots were quite popular.  The Crosley disc was a Goodyear development, a caliper type with ventilated disc, originally designed for aircraft applications.  
Chrysler developed a unique braking system, offered from 1949 to 1953. Instead of the disc with caliper squeezing on it, this system used twin expanding discs that rubbed against the inner surface of a cast-iron brake drum, which doubled as the brake housing. The discs spread apart to create friction against the inner drum surface through the action of standard wheel cylinders. Because of the expense, the brakes were only standard on the Chrysler Crown and the Town and Country Newport in 1950. They were optional, however, on other Chryslers, priced around $400, at a time when an entire Crosley Hot Shot retailed for $935. This four-wheel disc brake system was built by Auto Specialties Manufacturing Company (Ausco) of St. Joseph, Michigan, under patents of inventor H.L. Lambert, and was first tested on a 1939 Plymouth. Chrysler discs were "self-energizing," in that some of the braking energy itself contributed to the braking effort. This was accomplished by small balls set into oval holes leading to the brake surface. When the disc made initial contact with the friction surface, the balls would be forced up the holes forcing the discs further apart and augmenting the braking energy. This made for lighter braking pressure than with calipers, avoided brake fade, promoted cooler running, and provided one-third more friction surface than standard Chrysler twelve-inch drums. Today's owners consider the Ausco-Lambert very reliable and powerful, but admit its grubbiness and sensitivity.

Types of Disk Brake

Instead of traditional expanding breaks that press outward against a circular drum. Disk break utilize a cast iron rotor (disk) with brake pads positioned on either side of it. Breaking effect is achieved in a manner similar to the way squeeze a spinning disk between fingers.
There are three types of disk brakes:
·         A Fixed caliper
·         A Floating Caliper
·         A Sliding Caliper

A Fixed caliper
It is used one or two pistons mounted on each side of the rotor (in each side of the caliper). The caliper mounted rigidly and does not move. The following Image shows in detailed,
A Floating Caliper
Floating caliber use threaded guide pins and bushing, or a sleeve to allow the caliper to side and apply the brake pads.

The working of disk Breaks

Let's take a look at the basic disc brake system and how it works...
The components:
  • Master Cylinder
  • Steel brake lines
  • Proportioning valve
  • Brake calipers
  • Brake rotors or discs
  • Brake pads, anti-rattle hardware, and siding mechanisms (IE: pins)


1. The master cylinder is mechanically connected to the brake pedal through a system of steel rods called linkage. These rods operate at different angles using bushings that are usually made of nylon, rubber, or Teflon. When you step on the brake pedal, the linkage pushes on a steel rod that pushes into the back of the master cylinder. The master cylinder is nothing more than an elaborate pump that forces break fluid through the braking system to energize the various components that stop your car.
2. The steel brake lines are the infrastructure that provides a pathway for the brake fluid to travel through to do its job.
3. The Proportioning valve measures and adjusts the amount of fluid that goes to the front Vs. back brakes, because each set of brakes require different volumes and pressures to equally brake and stop the car.
4. The brake calipers are nothing more than powerful "C" clamps that are actuated by hydraulic pressure which occurs when the driver depresses the brake pedal, creating hydraulic pressure within the system. The calipers have large pistons inside of them that, when brake fluid pushes behind them, are forced outward ... creating a clamping action on the pads, which are in contact with the rotors.
5. Brake rotors or discs are flat round steel discs that are attached to the car's wheels. The calipers straddle over them and, when the brake pedal is depressed, the calipers clamp down on them, causing the brake pads to make contact with the rotors, creating friction and thus stopping the car.
6. Attached to the calipers are brake pads. They are the friction material that is needed to stop the forward motion of the wheels. Specifically, these pads are made of steel backing with friction material affixed to it, either by the use of industrial grade glue or steel rivets. Anti-rattle hardware consists of spring-steel clips that are affixed to the brake pads to keep them in place on the brake caliper. Without this hardware, the pads would rattle, causing clicking and squealing noises when the wheels are in motion. The sliding mechanisms are usually pins upon which the calipers slide. They are attached to the steering knuckle in such a way as to position the brake calipers so that they straddle the disc with the pads attached to them. When the brake pedal is depressed, the hydraulic pressure generated within the system forces the piston within the caliper outward; this causes the brake pads to clamp onto the discs, creating the friction necessary to stop the forward motion of the wheels. The sliding mechanisms must be clean, lubricated, and moveable for the calipers to apply and release the brake pads on the discs.




 References

·         http://arrc.ebscohost.com/ebsco_static/repairips/8852.htm#8852CH26_Disc_Brakes.htm

·         https://en.wikipedia.org/wiki/Disc_brake#Early_experiments